Jupiter is the largest planet in our solar system and contains more matter than all of the other planets combined. Jupiter has a composition much like the Sun, and the planet has Auroral emissions much like Earth's northern lights. Jupiter also has a ring system, but the rings are invisible from Earth.

On January 7, 1610 when Galileo observed Jupiter through his telescope, he thought he saw three stars near the planet, but later the stars appeared to move. Galileo observed four "stars" total, and later realized that the stars were actually moons. This was proof that everything in the uinverse did not revolve around the Earth.

According to NASA, German astronomer Simon Marius may have observed Jupiter's moons before Galileo, but did not publish his discovery. Galileo referred to the moons as the "Medicean planets" in homage to the Medici family. Marius had his own names for the moons, suggested to him by fellow German astronomer Johannes Kepler, and those are the ones we use today: Io, Europa, Callisto and Ganymede, three maidens and a boy beloved by the god Jupiter. These four moons are now known as the Galilean moons.

Jupiter has 62 known moons, but the Galilean moons, which are the four largest, are the most well known. Io, Euorpa, Ganymede, and Callisto may share a common host planet, but they are very distinct orbs.

Io is the most volcanically active body in the solar system. Jupiter affects the surface of Io very powerfully; according to NASA, the surface bulges inward and outward by as much as 330 feet. The incredible pressures that Jupiter brings to bear on Io is the primary cause of its volcanic activity. Io also cuts across Jupiter's magnetic field; the resulting radiation contributes to Jupiter's auroras.

Europa is thought to be covered by an ocean of salt water. Because Europa is so far from the Sun, the surface of the planet is completely frozen. NASA recently announced that it has plans to send a spacecraft to Europa to explore the possibility of life beneath the ice.

Callisto is the most heavily cratered moon in the solar system, it is thought to have almost no surface activity. Callisto's surface is dark compared with the other large moons of Jupiter, but it is brighter than the Earth's moon.